1. Field of the Invention
The present general inventive concept relates to a method and an apparatus to efficiently perform dynamic frequency selection (DFS), and more particularly, to a method and an apparatus to efficiently perform DFS between basic service sets (BSSs) which include wireless LAN stations that use a predetermined frequency band, for example, a 5 gigahertz frequency band, and which exist in the same channel, regardless of negotiation capability of a DFS owner.
2. Description of the Related Art
According to IEEE 802.11 and IEEE 802.11h standards, terms used in frequency selection are defined as follows.
A BSS (basic service set) is a communication area consisting of a group of any number of stations which communicate with each other in the same channel. Wireless LAN uses the BSS as a standard building block for communication.
A station is a basic component of the BSS and is any device capable of wireless communication.
A DFS owner is a station which detects radar operating in the same channel and then selects a new channel to switch to. In an independent BSS, any station can be a DFS owner.
As communication techniques rapidly develop, various methods of wireless communication are being used to cope with tasks usually performed by wired communication which necessarily requires wire. One method of wireless communication known as the IEEE 802.11 family of standards has recently become very prominent. IEEE 802.11 standard includes a/b/g/(n) amendments with respect to frequencies and methods of communication. The IEEE 802.11a standard uses a 5 gigahertz (GHz) band for communication. However, the 5 GHz band is already used by radar for meteorological observation, satellite navigation, and satellite communication, as well as for military purposes. International Telecommunications Union—Radiocommunications (ITU-R), European Telecommunications Standards Institute (ETSI), and Federal Communications Commission (FCC) acknowledge that wireless LAN using the 5 GHz band causes serious problems to radar and suggest that the effect on radar signals be minimized by using DFS or transmit power control (TPC). DFS is a method enabling a BSS to detect radar signals and resume communication in a new channel in which radar does not operate. The IEEE 802.11h standard defines for detecting radar signals and notifying constituents of a network of detected radar signals such that they may switch channels.
DFS according to the IEEE 802.11h standard is used to avoid a circumstance where a BSS operates on the same channel as radar and is limited to function when only one BSS exists. However, wireless LAN techniques have rapidly developed recently and a plurality of BSSs may exist in the same channel. Conventional techniques do not provide a protocol between BSSs, and as a result, all the BSSs affected by radar can switch channels out of an original channel and switch to the same new channel. As a result, the original channel may be emptied and quality of service (QoS) of the new channel may decrease to a level where appropriate communication may not be performed.
FIGS. 1A through 1D illustrate problems which may be caused by a conventional DFS when two or more BSSs exist together in the same channel or when two or more BSSs and radar exist together in the same channel.
FIG. 1A illustrates BSS1 and BSS2 existing in a same channel.
Referring to FIG. 1A, when BSS1 and BSS2 exist in a same channel A, each BSS is affected by communication of the other, thus QoS of the original channel drops below a predetermined level. Accordingly, appropriate communication may not be performed. To avoid this problem, a conventional DFS mechanism provides a method to switch channels. However, the conventional DFS mechanism does not provide a protocol between the BSSs in the same channel, and as a result, BSS1 and BSS2 cannot negotiate with each other to determine which channels to switch to. Therefore, BSS1 and BSS2 switch to new channels not knowing which channel the other BSS switches to.
FIG. 1B illustrates BSS1 and BSS2 of FIG. 1A which have switched channels according to a conventional DFS.
Referring to FIG. 1B, since BSS1 and BSS2 of FIG. 1A switch channels by a conventional DFS without information on which channel the other BSS switches to, both BSS1 and BSS2 can switch from channel A to channel B together. In this case, the same problems that the BSSs had in channel A may occur in channel B, and the channel switching is performed meaninglessly.
FIG. 1C illustrates BSS1 and BSS2 and radar existing in a same channel.
Referring to FIG. 1C, when BSS1 and BSS2 exist in a same channel A and the radar transmits in channel A, BSS1 and BSS2 have to switch to new channels to avoid the radar using a DFS mechanism. However, as in FIG. 1C, the conventional DFS mechanism does not provide a protocol between the BSSs in the same channel, and as a result, BSS1 and BSS2 cannot negotiate with each other to ascertain which channels to switch to. Therefore, BSS1 and BSS2 switch to new channels not knowing which channel the other BSS switches to.
FIG. 1D illustrates BSS1, BSS2 and the radar of FIG. 1C in which BSS1 and BSS2 have switched channels according to a conventional DFS.
Referring to FIG. 1D, BSS1 and BSS2 of FIG. 1C switch to new channels using a conventional DFS method without obtaining information regarding which channel the other BSS switches to. However, a BSS can detect radar prior to or posterior to channel switching in accordance with its capability. As illustrated in FIG. 1D, BSS1 can switch to channel B and avoid the radar, and thereby perform well, while BSS2 can detect the radar after a predetermined time, and as a result, remain in channel A.